Protozoal and epitheliocystis-like infections in the introduced

Work et al.: Pathology of bluestripe snapper in Hawaii
65
The high prevalence of protozoans in taape is of
concern because taape associate closely with native
Hawaiian goatfish and opakapaka. We suspect the
high prevalence of protozoa in taape could be, in part,
due to their bottom-feeding habits, thus providing
ample opportunity to ingest intermediate hosts. Future
studies should concentrate on assessing the risk of
extraintestinal coccidial infection in native fish that are
associated closely with taape and determining whether
these organisms infect taape in their native range in
the Marquesas.
In contrast to classical epitheliocystis infections that
occur in the gills, our finding of epitheliocystis-like
structures in kidney and spleen was unusual. Although
the light microscopic appearance and staining characteristics
(Gram negative and positive with Gimenez
stains) were similar to epitheliocystis found in the gills
of various fish (Crespo et al. 1999), the ultrastructural
appearance differed. Epitheliocystis are intracellular
round organisms, usually less than 1 µm in diameter,
with an electron-dense nucleopasm surrounded by an
electrolucent halo and electron-dense ribosomes, and
aggregates of epitheliocystis are surrounded by a thin
capsule (Paperna & Alves de Matos 1984, Crespo et
al. 1999). In contrast, the structures in taape had a
thick capsule surrounding a granular matrix containing
degenerating mitochondria. This matrix in turn
surrounded a thin inner membrane that contained numerous
spherical membrane-bound structures, ranging
in size from 1 to 3 µm in diameter with no evident
nuclear structure. Lack of nuclei or other membranebound
organelles lead us to suspect we are seeing a
prokaryote, hence our nomenclature of epitheliocystislike.
Taape with this organism formed a mononuclear
inflammatory response that appeared to progress to
chronicity with formation of a capsule of fibroblast
cells, and this inflammation appeared more severe
with age (data not shown). Similar capsules were occasionally
noted in pen-raised opakapaka in Hawaii
(Kent & Heidel 2001), suggesting that other native fish
may also be affected by this organism. Based on inflammatory
response, and drop in prevalence in larger
fish, we suspect these epitheliocystis-like organisms
may cause morbidity and mortality in taape. Prevalence
of infection with this organism was much lower
than for protozoa, again suggesting that survival of fish
infected with this organism may be low, or that opportunities
for infection are more limited. Future studies
will need to elucidate the identity of this structure, perhaps
by examining early- and late-stage infections.
One taape had cerebral organisms compatible in
morphology with myxosporeosis. Myxosporea of taape
were most similar in morphology to Henneguva (Lom
1984) based on the fusiform shape and bifurcate caudal
extensions. Definitive identification of these organisms
would require observations of spores in wetmount
preparations. Cerebral (Hedrick et al. 1998) and
muscle (Moran & Kent 1999) myxoporea cause severe
diseases in anadromous fish; however, given the low
prevalence of cerebral myxosporea in taape, we suspect
this parasite does not play a significant role in
diseases of taape.
Microsporidians were rarely seen and were not associated
with significant pathology, although microsporodians
are capable of infecting a variety of organs, causing
massive nodules (xenomas) in marine fish (Lom
1984, Shaw & Kent 1999). The presence of a variety of
trematodes was expected. Marine fish in Hawaii are
infected with many different nematodes and trematodes
(Yamaguti 1968, 1970, Rigby & Font 1997), and
based on low prevalence and minimal pathology, we
suspect these trematodes do not play a significant role
in the health of taape in Hawaii.
Acknowledgements. The authors thank Alvin Muranaka,
Gary Voitovich and the city and county of Honolulu for collecting
fish. This work was funded in part by the Water
Resources Division of the University of Hawaii. Thanks to F.
Murado, J. Winton and anonymous reviewers for constructive
comments.
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